Many methods have been suggested for enhancing the quality of tobacco filler material. These methods have included expansion of tobacco filler to increase the filling power of the tobacco and thereby reduce the delivery of tar and nicotine relative to a product made with unexpanded tobacco. In addition, methods have been proposed for preferentially changing the pyrolytic and flavor characteristics of smoking tobacco products, both by removal and by addition of various agents to tobacco.
The processes proposed for expanding tobacco have included incorporation of various agents into the tobacco. For example, tobacco has been contacted with a gas under somewhat greater than atmospheric pressure, whereby the tobacco cells are expanded. Other expansion methods which have been employed or suggested have included impregnation of tobacco with various liquids, which are driven off to expand the tobacco. Further, treatment of tobacco with solid materials which, when heated, decompose to produce gases which serve to expand the tobacco has been suggested. Still other methods of tobacco expansion have included treatment of tobacco with gas-containing liquids, such as carbon dioxide-containing water, under pressure followed by heating or pressure reduction. Treatment of tobacco with gases which react to form solid chemical reaction products within the tobacco, which may be then decomposed by heat to produce gases within the tobacco is another technique which has been developed for expansion of tobacco. In many of these methods, carbon dioxide has been employed as an expansion agent. More specifically:
In U.S. Pat. No. 1,789,435 to Hawkins, tobacco is expanded by contact with a gas, which may be air, carbon dioxide or steam under about 20 pounds of pressure. Thereafter, the pressure is released whereupon the gas which has penetrated the tobacco expands tending to increase the volume of the tobacco.
According to the method of British Pat. No. 1,331,640, tobacco is impregnated with a non-gaseous compound capable of liberating a gas, such as carbon dioxide, oxygen or ammonia, upon thermal decomposition. Preferred compounds are said to be those which decompose at relatively low temperature, including ammonium carbonates, ammonium carbamates, organic dicarboxylic acids and peroxides.
South African applications Nos. 70/8291 and 70/8292 to R. J. Reynolds Tobacco Company, both filed in 1970, relate to tobacco expansion with chemical compounds which decompose to form a gas or with inert solutions of a gas, under pressure to maintain the gas in solution until it impregnates the tobacco.
A patent to Robert G. Armstrong et al., U.S. Pat. No. 3,771,533 which is assigned to the same assignee as the assignee of the present invention, involves treatment of tobacco with carbon dioxide and ammonia gases whereby the tobacco is saturated with these gases and ammonium carbonate is formed in situ. The ammonium carbonate is thereafter decomposed by heat to release the gases within the tobacco cells and to cause expansion of the tobacco.
In copending U.S. Patent Application Ser. No. 891,468 to de la Burde et al., assigned to the same assignee as the instant application, a process for expanding tobacco is described comprising the steps of (1) impregnating tobacco with gaseous carbon dioxide under pressure of at least about 250 psig and at sufficient temperature that substantially all of the carbon dioxide is maintained in gaseous form, (2) decreasing the pressure on the carbon dioxide-impregnated tobacco and (3) heating the impregnated tobacco under conditions effective to liberate the carbon dioxide therein so as to cause expansion of the tobacco. Copending U.S. Application Serial No. 891,290 to Utsch and assigned to the same assignee as the instant application describes an improvement in this last process which comprises cooling the gaseous carbon dioxide and tobacco system in step (1) above to a temperature close to the saturation temperature of carbon dioxide but not lower than -23.degree. C. The conditions during this cooling are such that the carbon dioxide is not condensed to any significant degree, but rather remains substantially in the gaseous state.
Application Ser. No. 951,072 to Aument et al. filed on Oct. 13, 1978 and assigned to the same assignee as the instant invention, describes a process for impregnating tobacco with carbon dioxide which comprises: (a) contacting tobacco with carbon dioxide gas at relatively low pressure, (b) rapidly cooling the tobacco-carbon dioxide system until the carbon dioxide condenses and solidifies within the tobacco, and (c) releasing the pressure in the cooled system. Thereafter, the carbon dioxide-treated tobacco is expanded conventionally, such as by subjecting it to heating conditions effective to liberate the carbon dioxide therein.
Expansion of tobacco, using liquid carbon dioxide is described in Belgium Pat. No. 821,568, which corresponds to U.S. Application Ser. No. 441,767 to de la Burde and Aument and is assigned to the same assignee as the present application and in Belgium Pat. No. 825,133 to Airco, Inc. This process may be described as a process for expanding tobacco comprising the steps of (1) contacting the tobacco with liquid carbon dioxide (CO.sub.2) to impregnate the tobacco with the liquid carbon dioxide, (2) subjecting the liquid carbon dioxide-impregnated tobacco to conditions such that the liquid carbon dioxide is converted to solid carbon dioxide and (3) thereafter subjecting the solid carbon dioxide-containing tobacco to conditions whereby the solid carbon dioxide is vaporized to cause expansion of the tobacco.
A series of patents to Roger Z. de la Burde, U.S. Pat. Nos. 3,409,022, 3,409,023, 3,409,027 and 3,409,028, granted in 1968, relate to various processes for enhancing the utility of tobacco stems for use in smoking products by subjecting the stems to expansion operations utilizing various types of heat treatment or microwave energy.
In addition to its use as an expansion agent, carbon dioxide has also been used in the food industry as a coolant and, more recently, has been suggested as an extractant for food flavors. It has also been described in German Offenlegungsschrift No. 2,142,205 (Anmeldetag; August 23, 1971) for use, in either gaseous or liquid form, to extract aromatic materials from tobacco.
None of the above art, involving the use of carbon dioxide suggests its use as a means for uniformly incorporating additives, such as flavoring agents, into tobacco. Moreover, although a number of methods have been suggested for incorporating additives having a beneficial effect on the organoleptic properties of smoking tobacco products, none of these methods involve the use of carbon dioxide.
Such additives have commonly been materials which themselves flavor the product or materials which release flavorant agents upon pyrolysis. Such materials have included the 1-menthyl carbonate esters of various alcohols disclosed by Bavley et al. in U.S. Pat. No. 3,312,226, mixed carbonate esters of a flavorant and a polyhydroxy compound disclosed in Mold et al., U.S. Pat. Nos. 3,419,543 and 3,332,428 and Kalinanos et al., U.S. Pat. No. 3,449,452 and polymeric carbonate esters disclosed by Rundberg, Jr. et al. in U.S. Pat. No. 3,887,603 and by Van Auken et al. in copending U.S. applications, Ser. Nos. 728,729 filed Oct. 1, 1976, now U.S. Pat. No. 4,119,106 and 859,712, as well as many others.
Incorporation of flavorants or flavorant release agents into tobacco has typically been accomplished by dissolving the flavorant or agent in a suitable solvent. The solution of flavorant material is thereupon sprayed on the tobacco or injected into the tobacco matrix. The solvent selected depends on the particular flavorant material employed. Solvents have included water and various organic materials, such as alcohol, acetone or cyclohexane.
Flavorant materials have also been admixed with tobacco material in solid form. This may be accomplished, for example, by admixing the solid dry material directly with the components of reconstituted tobacco sheet prior to forming the sheet. Alternatively, flavorant material, encapsulated according to the method proposed in McGlumphy U.S. Pat. No. 3,550,598, has been incorporated into tobacco material using conventional techniques. For example, an aqueous slurry of such capsules may be sprayed onto tobacco. Adhesives or binders may be employed to bind the capsules to the filler.
A patent to John D. Hind, U.S. Pat. No. 3,425,425, granted in 1969, which is assigned to the same assignee as the assignee of the present invention, relates to the use of carbohydrates to improve the puffing of tobacco stems. In that process, tobacco stems are soaked in an aqueous solution of carbohydrates and then heated to puff the stems. According to the patent, the carbohydrate solution may also contain organic acids and/or certain salts which are used to improve the flavor and smoking qualities of the stems.
These previously employed techniques for incorporating additives for enhancing organoleptic properties of smoking tobacco products have not been found to be completely satisfactory. Distribution of additives on the tobacco fibers may often be uneven, and more importantly, full penetration of the added substances into the cellular structure may not be achieved. Removal of residual solvent is often a problem. Morever, where the tobacco material being altered has been expanded and the flavorant agent is added as a spray after expansion, collapse of the tobacco toward the unexpanded state may result.
Unexpectedly, it has been discovered that flavorant addition can be satisfactorily effected by means of the method described herein. The flavorant is uniformly distributed in tobacco material with full penetration into the cellular structure when the instant method is employed. Moreover, the present method not only avoids the disadvantages encountered in flavorant addition to expanded product, but, in fact, allows addition of flavorant and an expansion agent to be accomplished in a single step.